Organo silyl-silica filled siloxane elastomers and process for producing same



nited States Patent 6 ice 2863846 Flaizented Dec. 9, 1958 It 2 I viscosity of at least 10,000 cs. Such polymers range in 2,863,846 physical state from relatively fluid liquids to non-flowing ORGANO SILYL-STLTCA FILLED SILOXANE ELAS TOMER AND PROCl-ES FOR PRODUCING Leslie 5. Tyler, Midland, Mich, assignor to Dow Corning Corporation, Midland, Mich, a corporation of Michigan No Drawing. Application May 4, 1950 Serial No. 160,100

11 Claims. Cl. 260-37) This invention'relates to siloxane elastomers.

Most siloxane rubbers heretofore known are materials having efiiciencies of the order of 50 to 75. The efiiciency of a rubber is the product of its tensile strength in p. s. i. times the percent elongation at break divided by 1,000. An exception is the elastomers disclosed in the copending application of Earl L. Warrick, Serial No. 86,110, filed April 7, 1949, now Patent 2,541,137, and assigned to the assignee of this invention.

These rubbers have efiiciencies upwards of 150 and areprepared from special siloxane polymers and silica fillers. The reinforcing fillers employed therein havea heat of wetting by water of from 0.3 to 1 calorie per cc. of pore volume.

This invention relates to high efiiciency siloxane elastomers (i. e. efiiciencies upwards of 150) in which the special silica fillers have a heat of wetting by water-of less than 0.2 calorie per cc. of pore volume.

It is an object of this invention to produce siloxaneelastomers which have efficiencies upwards of 150. Another object is to provide high efficiency siloxane elastomers with improved crepe aging properties. Another object is to provide high etficiency siloxaneelastomers with higher durometer values than heretofore. obtained with such elastomers. Other objects and advantages will be apparent from the following description.

This invention relates to compositions of-matter com.- posed of a benzene soluble organopolysiloxane having. a

viscosity of at least 10,000 cs. and from to 100 parts" by weight based on theweight of 100 parts siloxane, of a silica filler having a pore volume of at least 3 cc. per gram. The filler is composed of organosilyl units of the formula RRSi: or R R'Si and SiO in the molar ratio of from .06 to .6. The organo silyl units are linked tothe silicon of the SiO through SiOSi linkages.

The elastomers of this invention are prepared by curing a mixture of siloxane and filler at a temperature between 100 C. and 400 C. until a non-tacky rubbery product is obtained. One such meth'od'is that of heating the mixture at 250 C. for 24 hours. The resulting elastomers normally have efficiencies in excess of 150. The curing time can be greatly reduced by employing organic peroxides as vulcanization catalysts. When peroxides are employed, the curing is effected by heating at a temperature above 110 C. for a few minutes. tacky product thus obtained may be aged at 200 C. to 250 C. to further improve its physical properties.

Peroxides which are employed as vulcanization catalysts are organic peroxides, such as benzoyl peroxide, tertiary butyl perbenzoate and tertiary butyl peracetate. The latter is described in the copending application of Earl L. Warrick, Serial No. 126,681, filed November 10, 1949, now Patent 2,572,227, which is assignedto the assignee of this invention. If peroxides are employed, it is preferable that they be used in amount less than 6 parts by weight per 100 parts of siloxane.

The elastomers of this invention are prepared frompolymers which are benzene soluble and-which have a The non soft solids. The polymers may be prepared by any-- of the well known methods for polymerizing siloxanes; The.

desired physical properties are not obtained with polymers having viscosities below 10,000-cs. or with benzene.

insoluble gums.

The organosiloxanes employed in this invention are those in which the organic groups aremethyl, ethyl, phenyl, trifiuoromethylphenyl [F CC H or siliconeopentyl [(CH SiCH radicals. Examples of,such siloxanes are dimethylsiloxane, diethylsiloxane. phenylmethylsiloxane, phenylethylsiloxane, ethylmethylsiloxane, siliconeopentylethylsiloxsiliconeopentylmethylsiloxane, ane, trifluoro-methylphenylmethylsiloxane, trifluoromethylphenylethylsiloxane or copolymers' thereof. In addition, the polymers may contain limited amounts of diphenylsiloxane units, bis-siliconeopnetylsiloxane units, bis-trifluoromethylphenylsiloxane units and siloxane units of the type RSiO and R SiO where R is any of the above organic radicals. In allthe polymers, at least 50 percent of the organic radicals are the defined, alkyl radicals and there are from 1.98 to '2 organic radicals per silicon atom.

Trifluo-romethylphenyl'siloxanes may be prepared by reacting F CC H Br with magnesium and thereafter coupling the resulting Grignard reagent with silicon tetrachloride, methyltrichlorosilane of ethyltrichlorosilane. The silanes are then hydrolyzed in the usual manner to the siloxane. Fluoromethylphenylsilanes are fully described and ;claimed in the copending. application of- Charles F. Kohl, Serial Number 130,857, filedDecember 2, 1949, now abandoned, and in U. S. Patents 2,640,066

and 2,640,063.

The fillers employed herein-are finely divided powders having a pore volume of at least 3 cos. per gram. They are composed of SiO linked to organo silyl units of the formulae RgRSiand RRSi: through SiOSi linkages. R is an alkyl radical of less than 5 carbonatoms and R is an alkyl radical of less than 5 carbon atoms or phenyl.

In order to produce high efiiciency siloxane elastomers the filler must have a pore volume of at least 3 cc. per gram .andthe molar ratio of organo silyl groups to SiO must be at least .06. The preferred molar range is from .08 to .25. i

The pore volume is the value determined by placinga weighed sample of the filler in a pycnometer, filling the pycnometer with octamethylcyclotetrasiloxane and determining, the ccs. of tetramer present by difference in Weight. The pycnometer is recharged with. a weighed" sample of the silica and filled with mercury. The volume of'mercury is determined. The volume of octamethyl cyclotetrasiloxane is, ccs. minus the volume of mercury in ccs. gives the pore volume in ccs. This is converted into ccs. per gram based upon the weight of the sample.

Methods of preparing the finely divided silicas are fully described in the applicants copending application Serial Number 160,099, now abandoned, filed concurrentlyherewith. The preferred method ofpreparation is that of reacting-silanes of, the formulae R RSiX and RRTSiX where X is chlorine or-alkoxy with a silica organogel having a. density of from .02 to .35 gram of Si0 per cc. ofgel. The solvent and excess silane are then removed by evaporation at a temperature-below the criticaltem-perature of the solvent. The resulting product is. a hydro,-

phobic powder having a pore volumeabove 3'.ccs.-' per.

"ram. c As is well known, silica ,organogels are prepared by replacing water in a silica hydrogel with an organic solvent. The solvent employed to make the silicas of this invention are those which are inert tothe above defined silanes.

Such solvents include ethers, hydrocarbons, chlorinated hydrocarbons, ketones and liquid completely condensed siloxanes.

The filler is employed in amount from 10 to 100 parts of the fillers shown in the Table II and in each case with 3 parts by weight tertiary butyl perbenzoate. The compounded polymer was cured by heating 5 minutes at 150 C. The resulting elastomers had the properties shown by weight filler based upon 100 parts by weight polymer. 5 below: In amounts below parts by weight little reinforcing is Table 11 obtained while loadings in excess of 100 parts produce dry crumbly materials which are difiicult to fabricate. Pom Mom The heat stability of the elastomers of this invention is F, C vphnne OTEUOJP Tensile IIIIII'CEHL hiltas good as that of heretofore known silicone rubbers. In 10 l or ompomm igg tg g L h g l addition, they possess a combination of high tensile 5102 i strength, percent elongation and durometer values heretofore unknown in siloxane elastomers. W i f? One of the difiiculties encountered with siloxane elasigiiiiistgigzjjjjjjjj "iii tomers filled with the heretofore known reinforcing fillers, 15 such as silica aerogels and fume silicas is that the com- EXAMPLE 4 pounded material would set at room temperature prior to vulcanization. Thus, the compounded material (i. e. the A dlmsthylpolyslloxane havmg vlscosny of 1401000 cs. at C. was compounded with 45 parts by weight unvulcanlzed polymer contalnmg fillers with or without of a finer havin a one Volume of 4 58 CCS er ram ,md peroxides) would become tough and elastic upon standing. 20 a Com osmon i h Hm 5 of As a result, after a week or two, the material could not 156 i with 3 arts 2 Wei ht a 1 eroxidc based be molded or extruded into tha dash-5d Shape This uni on the wei ht of the siloi tane g Th coni o iind d mixture desirable property interferes with the commercial handling hrat mold 5 i g I of such materials. The disadvantage is completely overg i g g g i a g g s fs i f s a come by employing the fillers of this invention. .3 t k f 633 8. Minor amounts of other additives which are normally Onga Ion a Tea 0 is c Clancy was employed in siloxane rubbers may be incorporated in the EXAMPLE 5 Products flhi5inV6nti0H- These P l? A non-flowing benzene soluble polysiloxane having a mems t0 the dcslred Color and matfirlals to plasticity of 88 mils and a composition of 5 mol percent Prove a Specific P p Such as comprfisslon An phenylmethylsiloxane and 95 mol percent dimethylsiloxexample of the latter is zinc peroxide. However, these ahe was compounded with 5 parts f the n f minor additives do not alter the essential characteristics of Example 4 and with 2 percent by weight tertiary hutyl the elastomers nor is their utility dependent thereon. perhehzoate' The compounded material was heated 5 The Plasticity Values given for the P y p y minutes at 140 C. and thereafter cured 24 hours at below were determined in accordance with ASTMD C The resulting elastomer had a tensile Strength 926-471 with the exception that a 4.2 gram sample was f 332 i., percent elongation at break of 320 and employed instead of the 2 cc. sample called for in the an ffi i f standard test.

The following examples are illustrative only. EXAMPLE 6 EXAMPLE 1 40 A polymeric dimethylsiloxane having a plasticity of 113 mils was compounded w1th 30 parts by wclght of benzene Soluble copolymenc 5110x3115 having a the filler of Example 4 and with 3 parts by weight ter- Posmon of mol Percent Phenylmethylsfloxane Q tiary butyl perbenzoate. The compounded material was mol percent dimethylsiloxane and having a plasticity of heated 5 minutes at 0 in a mold and the resulting 80 was compmmded with Parts of a silica elastomer had a tensile strength of 645 p. s. i., an elonhavmg a Pore volume of per gram The finer gation at break of 430 percent and an efliciency of 277. was composed of (CH Siand SiO in the molar ratio of 0.156. The compounded material was molded 5 min- EXAMPLE 7 utes under 60 pounds steam and then heated 24 hours at A copolyrneric siloxane having a plasticity of mils 250 C. The resulting elastomer had an efliciency of 290. e and a composition of 3.5 mol percent phenylmethylsiloxane and 96.5 mol percent dimethylsiloxane was com- EXAMPLE 2 pounded with 81 parts by weight of the tiller of Example The various silica fillers having the composition shown 4, d 3 parts b i h tertiary b l perbcnzoatc, Th in Table I, where each is compounded with the siloxane compounded i l was h d 5 minutes at C of Example 1 in amount of 30 Parts y Weight filler l and the resulting elastomer had a tensile strength of 100 Parts p y 3 Parts y Weight tertiary bull/1 P 55 561 p. s. i. and an elongation at break of 795 percent. benzoate based upon the siloxane was incorporated and Th fii i was 445 the compounded material was heated at C. for 5 minutes. The properties of the resulting elastomers are EXAMPLE 8 shown below. Elastomeric products having high efficiencies are ob- Table I Pore Molar volume ratio Tensile Percent Filler Composition in cc Organosilyl in p. s. 1. Elongation Efficiency per g. groups to slot (CHi):lSlO1.. 421 440 4. 409 403 104 4.5-. 898 633 560 above 3.5.. .08.. 659 460 303 0113(0511951-5102 above3.5.. above .08.. 390 368 13s EXAMPLE 3 The critical nature of pore volume is shown by the following example. The copolymeric siloxane of Examtained when any of the siloxanes shown below are compounded with 45 parts by weight of the filler of Example ple 1 was compounded with 30 parts by weight of each 75 1 and with 3 parts by weight of either benzoyl peroxide 5. or tertiary butyl peracetate andthereafter heated for 15 minutes at 140 C.

Composition in mol percent: Plasticity in mils 10 (C H SiO, 90 (CH SiO 90 5 C H (C H )SiO, 95 (CH SiO 100 2.5v (C' H SiO, 97.5 (CH SiO 90 10 [(CH SiCH ]CH SiO, 90 (CH SiO 85 40 C H (CH ')SiO, 60 (CH SiO 110 EXAMPLE 9 .02 mol of the cyclic tetramer of bis-trifluoromethylphenylsiloxane and 0.98 mol of the cyclic tetramer of dimethylsiloxane were copolymerized by heating with potassium isopropoxide in amount of one potassium atom per 5,000 silicon atoms at 150 C. to 160 C. for minutes. The copolymer was cooled to room temperature and 4 percent by weight of fuming sulfuric acid was added. After 5 to 10 minutes at room temperature the viscosity had increased. 2 percent by weight water was added and the viscosity continued to increase at room temperature until a solid benzene soluble polymer was obtained.

This polymer was milled with 40 parts by weight of the silica filler of Example 4 and with 4 parts by weight tertiary butyl perbenzoate and thereafter heated 10 minutes at 150 C. in a mold. The resulting elastomer had a tensile strength of 910 p. s. i., an elongation at break of 850 percent and an elficiency of 772.

That which is claimed is:

1. A method of preparing a siloxane elastomer which comprises heating a mixture of a benzene soluble organopolysiloxane having a viscosity of at least 10,000 cs. at C., in which siloxane the organic radicals are selected from the group consisting of methyl, ethyl, phenyl, trifluoromethylphenyl and siliconeopentyl radicals, at least 50 percent of said radicals being alkyl and there being from 1.98 to 2 said organic radicals per silicon atom, and from 10 to 100 parts by weight of a filler based upon 100 parts by weight siloxane, said filler having a pore volume of at least 3 ccs. per gram and being composed of Si0 and organosilyl units selected from the group consisting of RRSi and R R'Si, where R is an alkyl radical of less than 5 carbon atoms and R is selected from the group consisting of alkyl radicals of less than 5 carbon atoms and phenyl radicals, in amount such that the molar ratio of said organosilyl units to SiO is from .06 to .6, said organosilyl units being attached to the silicon atoms of the Si0 through SiOSi linkages, at a temperature from 100 C. to 400 C. until a coherent nontacky rubbery product is obtained.

2. A method of preparing a siloxane elastomer which comprises heating a mixture of a benzene soluble organopolysiloxane having a viscosity of at least 10,000 cs. at 25 C., in which siloxane the organic radicals are selected from the group consisting of methyl, ethyl, phenyl, trifluoromethylphenyl and siliconeopentyl radicals, at least 50 percent of said radicals being alkyl and there being from 1.98 to 2 of said organic radicals per silicon atom, from 10 to 100 parts by weight of a filler based upon 100 parts by weight siloxane, said filler having a pore volume of at least 3 ccs. per gram and being composed of SiO and organosilyl units selected from the group consisting of RRSi: and R RSi, where R is an alkyl radical of less than 5 carbon atoms and R is selected from the group consisting of alkyl radicals of less than 5 carbon atoms and phenyl radicals, in amount such that the molar ratio of said organosilyl units to SiO is from .06 to .6, said organosilyl units being attached to the silicon atoms of the S10 through SiOSi linkages and an organic peroxide selected from the group consisting of benzoyl peroxide, tertiary butyl perbenzoate and tertiary butyl peracetate, in amount less than 6 parts by Weight based upon the weight of the siloxane, at a temperature between 110 C. and 400 C. until a non-tacky coherent rubbery product is obtained.

3. A heat curable composition ofmatter composed 10f a benzene soluble organopolysiloxane having a; viscosity of at least 10,000 cs. at 25 C. in which siloxane the organic radicals are selected from the group'consistingof methyl; ethyl, phenyl, trifluoromethylphenyl and siliconeopentyl radicals, at least 50 percent of said radicals being alkyl and there being from 1.98 to 2 of said organic radicals per silicon atom and from 10 to parts by Weight of a filler based upon 100 parts by weight siloxane, said filler having a pore volume of at least 3 ccs. per gram and being composed of SiO and organosilyl unitsselected from thegroup consisting of RRSi: and R RSi where R is an alkyl radical of less than 5 carbon atoms andR is selected from the group consistingof alkyl radicals .of less than 5 carbon atoms and phenyl radicals, in amount such that the molar ratio of said organosilyl units to SiO is from .06 to .6, said organosilyl units being attached to the silicon atoms of the Si0 through SiOSi linkages.

4. A composition of matter in accordance with claim 3 in which the organopolysiloxane is dimethylpolysiloxane.

5. A heat curable composition of matter composed of a benzene soluble organopolysiloxane having a viscosity of at least 10,000 cs. at 25 C., in which siloxane the organic radicals are selected from the group consisting of methyl, ethyl, phenyl, trifluoromethylphenyl and siliconeopentyl radicals, at least 50 percent of said radicals being alkyl and there being from 1.98 to 2 of said organic radicals per silicon atom, and from 10 to 100 parts by weight of a filler based upon 100 parts by weight siloxane, said filler having a pore volume of at least 3 ccs. per gram and being composed of SiO and organosilyl units selected from the group consisting of RR'Si and R R'Si in which R is an alkyl radical of less than 5 carbon atoms and R is selected from the group consisting of alkyl radicals of less than 5 carbon atoms and phenyl radicals, in amount such that the molar ratio of said organosilyl units to SiO is from .06 to .6, said organosilyl units being attached to the silicon atoms of the SiO through SiOSi linkages and an organic peroxide selected from the group consisting of benzoyl peroxide, tertiary butyl perbenzoate and tertiary butyl peracetate in amount less than 6 parts by weight based upon the weight of the siloxane.

6. A composition of matter in accordance with claim 5 in which the organopolysiloxane is a methylphenylsiloxane in which at least 50 percent of the radicals are methyl and in which the filler is composed of trimethylsilyl units and SiO in amount such that the molar ratio of said organosilyl units to SiO is from .08 to .25.

7. A composition of matter in accordance with claim 5 in which the organopolysiloxane is dimethylpolysiloxane.

8. A siloxane elastomer composed of a benzene soluble organopolysiloxane having a viscosity of at least 10,000 cs. at 25 C., in which siloxane the organic radicals are selected from the group consisting of methyl, ethyl, phenyl, trifiuoromethylphenyl and siliconeopentyl radicals, at least 50 percent of said radicals being alkyl and there being from 1.98 to 2 of said organic radicals per silicon atom and from 10 to 100 parts by weight of a filler based upon 100 parts by weight siloxane, said filler having a pore volume of at least 3 ccs. per gram and being composed of SiO and organosilyl units selected from the group consisting of RRSi: and R RSiin which R is an alkyl radical of less than 5 carbon atoms and R is selected from the group consisting of alkyl radicals of less than 5 carbon atoms and phenyl radicals in amount such that the molar ratio of said organosilyl units to SiO is from .06 to .6 said organosilyl units being attached to the silicon atoms of the SiO through SiOSi linkages.

9. A siloxane elastomer in accordance with claim 8 in which the organopolysilo-xane is a methylphenylsiloxane in which at least 50 percent of the radicals are methyl and in which the filler is composed of trimethylsilyl units and SiO in amount such that the molar ratio of trimethylsilyl units to SiO is from .08 to .25.

10. A siloxane elastomer in accordance with claim 8 in which the organopolysiloxane is dimethylpolysiloxane.

11. A heat curable composition of matter composed of a benzene soluble methylphenylpolysiloxane having a viscosity of at least 10,000 cs. at 25 C. in which siloxane there is from 1.98 to 2 methyl and phenyl radicals per silicon atom, at least 50 percent of said radicals being methyl and from 10 to 100 parts by weight of a filler based upon 100 parts by Weight siloxane, said filler having a pore volume of at least 3 cos. per gram and being composed of trimethylsilyl units and SiO in amount such that the molar ratio of trimcthylsilyl units to 510 is from .08 to .25, said silyl units being attached to the silicon atoms of the SiO; through SiOSi linkages.

References Cited in the file of this patent UNITED STATES PATENTS Krieble et al May 11, 1948 Wright Oct. 26, 1948 Warrick Feb. 1, 1949 Warrick Feb. 13, 1951 Safford Aug. 7, 1951 Bidaud Sept. 11, 1951 Warrick Aug. 26, 1952 Tc Grotenhuis Sept. 9, 1952 

3. A HEAT CURABLE COMPOSITION OF MATTER COMPOSED OF A BENZENE SOLUBLE ORGANOPOLYSILOXANE HAVING A VISCOSITY OF AT LEAST 10,000 CS. AT 25*C. IN WHICH SILOXANE THE ORGANIC RADICALS ARE SELECTED FROM THE GROUP CONSISTING OF METHYL, ETHYL, PHENYL, TRIFLUOROMETHYLPHENYL AND SILICONEPENTYL RADICALS, AT LEAST 50 PERCENT OF SAID RADICALS BEING ALKYL AND THERE BEING FROM 1.98 TO 2 OF SAID ORGANIC RADICALS PER SILICON ATOM AND FROM 10 TO 100 PARTS BY WEIGHT OF A FILLER BASED UPON 100 PARTS BY WEIGHT SILOXANE, SAID FILLER HAVING A PORE VOLUME OF AT LEAST 3 CCS. PER GRAM AND BEING COMPOSED OF SIO2 AND ORGANOSILYL UNITS SELECTED FROM THE GROUP CONSISTING OF RR''SI= AND R2R''SI WHERE R IS AN ALKYL RADICAL OF LESS THAN 5 CARBON ATOMS AND R4 IS SELECTED FROM THE GROUP CONSISTING OF ALKYL RADICALS OF LESS THAN 5 CARBON ATOMS AND PHENYL RADICALS, IN AMOUNT SUCH THAT THE MOLAR RATIO OF SAID ORGANOSILYL UNITS TO SIO2 IS FROM .06 TO 9, SAID ORGANOSILYL UNITS BEING ATTACHED TO THE SILICON ATOMS OF THE SIO2 THROUGH SIOSI LINKAGES. 